The present invention relates to an erase method and a soft programming method of a non-volatile memory device.
Recently, there are increasing demands for non-volatile memory devices which can be electrically programmed and erased and do not need the refresh function of rewriting data at certain intervals.
A non-volatile memory device generally includes a memory cell array in which cells for storing data therein are arranged in matrix form, and a page buffer for writing memory into specific cells of the memory cell array or reading memory stored in a specific cell.
Here, an interference phenomenon in which the threshold voltage is changed depending on a change of the threshold voltage of peri cells can be generated in a non-volatile memory cell. The greater the threshold voltage of peri cells changes, the greater the interference phenomenon occurs.
As a method of reducing the interference phenomenon, there has been known a method of improving the distributions of the threshold voltage of an erased cell by making the threshold voltage close to 0V to the greatest extent. Through this distribution, a change of the threshold voltage when peri cells are programmed can be reduced.
However, when program disturbance occurs due to this method, a margin is reduced. In particular, due to the program disturbance, the outermost cell adjacent to each select transistor has a greater threshold voltage change than that of other cells. Consequently, disturbance failure occurs in the outermost cell.
Electron-hole pairs are formed at a portion where the gate of each select transistor is overlapped with the junction by a gate induced drain leakage (GIDL) phenomenon. Electrons generated at this time are accelerated toward a channel because of a high channel boosting voltage. Accordingly, electrons move to the floating gate due to a soft program voltage applied to the word line of the outermost cell, therefore, the threshold voltage of a cell is increased. If the threshold voltage becomes higher than a specific voltage, a disturbance phenomenon where an erase state of cells shift to a program state is generated.